SQL casts unwrap instead of hooking into error handling system

[mwylde]

Our SQL cast expressions currently deal with errors by unwrapping:

arroyo/arroyo-sql/src/expressions.rs

Line 1243 in 39c1bd6

parse_str(&StructField::data_type_name(output_type)).unwrap();

Causing an error on invalid cast is inline with the behavior of postgres, however we should find a way to hook into the error-reporting system to let the user know why the job failed. We may also want to support something like try_cast that attempts to cast and returns null if it fails.